1. Field of the Invention
The invention relates to a tubular cellulose-hydrate-based food casing, the inside of which is impregnated with liquid smoke. The casings are particularly suitable for encasing meat products such as sausage and ham. The invention further relates to processes for producing these food casings and to methods of their use.
2. Description of Related Art
Tubular cellulose-hydrate-based food casings have long been known. Such casings are usually produced by the viscose process. In this process, an alkaline solution of cellulose xanthogenate, generally termed a viscose solution, is extruded through a tubular or slot die, coagulated as cellulose hydrate gel using an acidic liquid, and regenerated to give cellulose hydrate. The unreinforced cellulose hydrate material thus produced is also termed transparent cellulose hydrate film and is known under the trade mark Cellophane.RTM.. In the production of fiber-reinforced casings, a tubular or web-shaped fibrous material is impinged with the viscose solution and then treated in a corresponding manner with coagulation liquid and regeneration liquid.
Food casings, even after relatively long storage times, must still be pliable and sufficiently extensible. Attempts have been made to improve these properties by addition of secondary softeners, such as glycerol. Since these softeners are not chemically bound to the cellulose hydrate but are only bound by intermolecular forces, they are leached out when the casing is soaked or when the sausage is scalded or cooked. This causes a particularly intense embrittlement of the softener-free dried cellulose casing after the processing. This phenomenon is due to crystallization proceeding in the cellulose material, leading to development of hydrogen bonding between the individual cellulose molecules in the cellulose structure and thus to convergence and spatial fixation. As a result of this structural change, the casing becomes particularly sensitive to impact and frequently tears over the entire length on first incision. According to EP-A 0 460 348, glycerol-free sausage casings which are produced with a mixture of cellulose and alginic acid and/or alginate, in contrast, show markedly improved properties.
Food casings must take the most varied requirements into account. They serve equally as a container during the processing of the product and as a protective casing for the finished product. However, appearance and flavor of the foods are decisive for sales. This particularly applies to smoked meat products. There is a trend to replace traditional smoking by the use of so-called "liquid smoke solutions" which have been developed by the food industry. These solutions have previously been incorporated into the meat mixture or sausage mixture or sprayed thereon. Because of the frequently uneven smoked color on the surface of the product and the deficient aroma, other methods have been sought. Thus attempts have been made to apply the liquid smoke solution onto the inner or outer surface of the food casings and thus to achieve the desired smoked color and the aroma being transferred to the filling.
According to DE-A 10 99 326, sausage casings made of regenerated cellulose are exposed during or after the drying process to the action of smoke which was generated by combustion of wood to a greater or lesser extent. The smoke produces resistance to the destructive action of microorganisms. The time of action is reduced if the cellulose tube is impregnated from the outside with the condensates produced from the wood smoke in concentrated or dilute form.
Liquid smoke, as obtained by introducing wood smoke into water, is acidic and can therefore damage the cellulose hydrate sausage casing. Such an acidic liquid smoke having a total acid content of at least 6% by weight, preferably at least 9% by weight, is disclosed in U.S. Pat. No. 4,377,187. A relatively high acid content denotes here a relatively high content of tar-like constituents. The inner or outer surface of the cellulose casings is impregnated by this liquid smoke.
In order to avoid damage to the cellulose, according to U.S. Pat. No. 4,834,993, the outer surface of cellulose-based sausage casings is treated with a neutralized liquid smoke which has a pH of greater than 4, preferably 5 to 9. In order to enable the diffusion of high-molecular constituents through the sausage casing, the neutralized liquid smoke can also contain a short-chain alcohol. However, in the neutralization of the liquid smoke, solid constituents generally precipitate out. In order to prevent this, at least 10% by weight of a water-soluble alcohol, such as ethanol, glycerol, propylene glycol or triethylene glycol, were added to the aqueous liquid smoke solution (See DE-A 28 13 796 equivalent to U.S. Pat. No. 4,104,408). The tar-like constituents precipitating out during neutralization redissolve if the pH of the liquid smoke solution is increased to greater than 10 (U.S. Pat. No. 4,446,167).
The alkaline liquid smoke solution can additionally further contain up to 10% by weight of glycerol and/or propylene glycol as softener for the sausage casing. In order to improve the peelability of the casing, the liquid smoke solution can further contain 0.5 to 2% by weight of carboxymethylcellulose, alginate, dextrin, amylopectin or other substances usual for this purpose (See U.S. Pat. No. 4,442,868). These substances can also be applied to the casing before the treatment with liquid smoke.
The tar-like constituents can be removed from the acidic liquid smoke by extraction with organic solvents. The color-imparting constituents of the smoke remain in the aqueous phase. Before further use, the aqueous phase is adjusted to a pH of 6 to 8 by addition of alkaline neutralizing agents. The same result is achieved if the acidic liquid smoke is neutralized and the tar-like constituents which precipitate out during this are separated off. A liquid smoke produced in this way is stable at neutral pH even without addition of alcohols or other additives (See EP-A 0 095 616). However, it has only a little smoke flavor, or none at all, so that the aroma must be transferred to the filling in another way.